1. Field of the Invention
The invention relates to solar collector for heating a fluid, e.g, water or air.
2. Discussion of the Prior Art
The use of solar collectors for heating fluids, e.g., water or air has been recognized in the prior art.
In U.S. Pat. No. 3,102,532 there is taught a solar collector including an outside and an inside glass sheet separated by a dead airspace. The inside glass sheet is separated from a bottom plate to provide a collector chamber that contains stacked sheets of perforated foil having their surface facing the sun painted black and the opposite surface provided with a reflective surface. Air is moved through the stacked sheets and heated by solar and infrared energy.
Although the solar collector taught in U.S. Pat. No. 3,012,532 is suitable for heating air, it has drawbacks. For example, providing stacked sheets of perforated foil is expensive. This is because each of the sheets has to be perforated and selectively coated. Another drawback is that not all the coated surfaces of the sheets are exposed to solar energy. This is because the upper sheets act as a barrier for solar radiation to the lower sheets. Therefore it can be assumed that the bottommost sheet of the stack is cooler than the topmost sheet. With this condition, there is a temperature gradient in the air flow which can result in the heated air having air masses of different temperatures instead of uniformly heated air.
U.S. Pat. Nos. 2,601,905 and 3,412,728 each teach a solar heating system which provides for the introduction of fresh air. In general, U.S. Pat. No. 3,412,728 teaches a solar collector having an outer transparent covering and a heat collector sheet, e.g., a corrugated metal sheet treated on its outer surface to absorb sunrays and convert them to infrared heat. An inner insulation member, e.g., glass fiber, or reflective insulation, is provided in spaced relation to the absorber. The transparent covering is provided with passages to admit warm air from outside to inside the collector.
The collector of U.S. Pat. No. 3,412,728 has limitations because the solar collector is not a closed system. More particularly, when fresh warm air enters the collector, there are conduction and/or convection heat losses which reduce the efficiency of the solar heat collector.
It would be advantageous therefore to provide a solar air heater that does not have the drawbacks of the prior art.